I searched and I may have misremembered the free version seems to have been around since the start except that the free version was initially invite and desktop only. Eventually everyone could use it but still only on desktop. The free version was even more limited back then it seems with a limit on how many hours you could listen to each month.

I could personally never use it. Because it was so incredibly limited. Not being allowed to skip tracks makes it unusable and I’m genuinely surprised anyone used it apart from trying the service.